Mounting means for carbon electrodes or graphite electrodes



Jan. 6, 1959 E. DOETSCH AL r 2,867,786 MOUNTING MEANS FOR CAR ELECTRODESOR GRAPHITE ELECTRODES Filed April 26. 1956 2 Sheets-Sheet 1 fflvenfor'sfk/vsr DOETJCH Arno? Jan. 6, 1959 E. DOETSCH ET AL 2,867,786 MOUNTINGMEANS FOR CARBON CTRODES OR GRAPHITE ELECTRO Filed April 26, 1956 2Sheets-Sheet 2 fen 6r .Oosnscw 4 6195608 A4 05/? frequently give rise tobreakdowns.

United Stats Patent O F MOUNTING MEANS FOR CARBON ELECTRODES OR GRAPHITEELECTRODES Ernst Doetsch, Numberg, and Gregor Klier, Schwaig, nearNurnberg, Germany, assignors to C. Conradty, Numberg, Germany, apartnership Application April 26, 1956, Serial No. 580,879 Claimspriority, application Germany April 29, 1955 6 Claims. (Cl. 339-263) Ourinvention relates to improved mounting means for carbon electrodes orgraphite electrodes of the type used in ovens heated by an electricalarc and, more particularly, to nipple connections for such electrodes.

Experience has shown that such nipple connections When the nippleconnection becomes loose the nipples are liable to be overheated as, insuch event, they must conduct the entire current, whereas in normaloperation the nipples only carry a portion or about thirty percent ofthe current, provided that the end faces of the electrodes and thecooperating end faces of the conductors are held by the nipple inperfect contact with a satisfactory pressure en-' gagement. Theoverheating of the nipple is liable to cause breakage of the same sothat the electrodes will come apart. This, however, has disastrousconsequences for the operation of the oven. The least that is liable tohappen is a restriction of the electrode conductor owing to increasedoxidation of the electrode material, such restriction involving apermanent risk of breakage and increasing the rate of consumption of theelectrodes.

Where conical nipples are employed which may be tightened in aparticularly simple manner by a turn of about two revolutions only, thenipples are particularly liable to become loose and to consequently comeoff.

A cause for the nipples becoming loose may be either the mounting of theelectrodes by unskilled laborers or vibration of the oven. To safeguardthe connection established by the nipples, it has been proposedheretofore to insert pins of carbon or graphite at the point ofconnection either into the end faces of the electrodes or at a certaindistance therefrom through the nipple boxes up to a bore of the nippleso that relative rotation cannot be effected.

Apart from the additional cost of labor the nipple box is weakened bysuch arrangement, since caloric stresses may cause cracks that originatein the bore. Moreover, experience has shown that such securing pinscannot prevent the co-operating end faces from being slightly spacedthus causing overheating of thenipples as previously explained.

The type of thread most frequently used on an international scale forgraphite electrodes, is the so-called trapezoidal thread, which has aconstant diameter, but which for conical nipples is modified toconstitute a trapezoidal thread having a diameter that varies as theconical cross section varies. With this type of thread the machiningused heretofore resulted in smooth surfaces. Because of the lubricatingproperties of the graphite the smooth surfaces will easily slide uponeach other, particularly where the oven is subject to powerfulvibrations, thus causing the nipple connection to become loose.

One feature of the present invention is electrodes of carbon or ofgraphite in which the current-conducting co-operating surfaces of thethreads of the nipples and of the electrodes have a structure reducingthe tendency of the thread to become loose and reducing the transitionalelectrical resistance at the same time.

, 2,867,786 Patented Jan. 6, 1959 According to another feature of theinvention the threads of the nipples and electrodes are profiled.Experience has shown that such profiled surfaces will interlock in sucha manner as to prevent accidental relative displacement.

The thread surfaces may be profiled in any suitable manner. Thus,according to a further feature of the invention said surfaces may be e.g. roughened, toothed, undulated or corrugated.

According to still another feature of the invention the end faces of thenipples and the electrodes respectively engaging each other may also betreated in a similar manner as stated for the co-operating surfaces ofthe threads.

It is a particular advantage of our invention that it can be applied toexisting types of threads that conform to international standards, andthat when the novel method is applied to a nipple connection it does notrequire additional steps of assembly and does not result in additionalcost.

In the accompanying drawing,

Fig. 1 represents a fragmentary longitudinal section of a cylindricalnipple and illustrates the normal type of thread, 1

Fig. 2 is a fragmentary longitudinal section of a cylindrical nippleproduced in accordance with the present invention,

Fig. 3 corresponds to Fig. 1 but shows the normal thread of a conicalnipple,

Fig. 4 corresponds to Fig. 2 but shows the thread of a conical nippletreated in accordance with the present invention, t

Fig. 5 is a fragmentary perspective view of a cylindrical nipple havingnormal threads, and

Fig. 6 is likewise a fragmentary perspective View of a cylindricalthreaded nipple but having threads formed in accordance with the presentinvention.

Figs. 79 are fragmentary, sectional, perspective views of electrodesadapted to co-operate with nipples according to Figs. l-6, said figuresshowing three different kinds of profiled thread surfaces.

Figs. 1 and 3 illustrate a normal type of thread of a cylindrical nippleand of a conical nipple respectively which may be, according to theinvention, modified by having the current-conducting co-operatingsurfaces a of the threads of the nipples profiled by roughening, asillustrated in Figs. 2 and 4 respectively. Such roughening may be madeby treating the respective surfaces with sand jets or jets of siliconcarbide.

Fig. 7 shows an electrode b having its thread faces 0 roughened. Ofcourse, the co-operating surfaces of the nipple and the electrode may beprofiled in any other suitable way, e. g. said co-operating surfaces maybe provided with teeth, as shown on thread faces d of the electrodeshown in Fig. 8 of the drawing.

According to another modification the co-operating surfaces may beundulated in the manner shown in Fig. 6 of the drawing respectively orcorrugated as shown in the embodiment of the electrode shown in Fig. 9'of the drawing.

This embodiment differs from that shown in Fig. 6 in that the corrugatedgrooves of the threads e are annular while in the embodiment accordingto Fig. 6 these grooves extend radially.

Of course the peripheral surfaces of the threads of the nipples as wellas of the cooperating surfaces of the electrodes may be roughened inaccordance with any one of the previously described embodiments.

In addition to the surfaces of the threads of the nipples and of theelectrodes, the meeting end faces of the nipples and the electrodes maybe treated as shown in Figs. 7-9; an end face 1 being shown in Fig. 7 asroughened; an end face g being shown in Fig. 8 as toothed, and an endface h being shown in Fig. 9 as annularly corrugated.

The corrugated surfaces may be produced by milling the normal surfaceswith a rotary milling tool having a slightly eccentric mounting and thusproducing rhythmic'a'l irregularity.

When a normal nipple and electrode are screwed together, the smoothsurfaces slide upon each other and 'areliable to become loose because ofa lubricating effect peculiar to graphite, but when such surfaces areprovided with corrugations of short wave length to form crests andrecesses, these corrugations will interlock when the thread is tightenedwhereby a natural safeguard against loosening of the connection isattained.

Another advantage of this method resides in the fact that it results insavings which offset any additional cost.

By constructing the thread faces and the end faces in 'acco'rda'nce'withthe presentinven'tion the electrode connection is not only securedagainst accidental loosening, but will also result in a considerablereduction of the transitionalelectrical resistance by increasing thecontact-surface area and the contact pressure, whereby current lossesare reduced and an unnecessary heating of the electrical conductors andthe consequent oxidation is avoided.

"We claim:

1. A nipple connection for electrodes of carbon or graphite comprisingthreads with current-conducting co operating surfaces for the nipplesand the end faces of the electrodes, and means formed integral with thesurfaces before assembly of the nipples and electrodes to reduce thetendency of the thread becoming loose and to reduce the electricalresistance therebetween'to a value below that of smooth-surfaceelectrode threads and end faces of corresponding size.

2. A nipple connection for electrodes according to claim 1, in which thesurfaces are undulated.

3. A nipple connection for electrodes according to claim 1, in which thesurfaces are tooth-shaped in cross section.

4. A nipple connection for electrodes according to claim 1, in which thesurfaces are corrugated.

5. A nipple connection for electrodes according to claim 1, in whichthe'surfaces are roughened.

6. A screw-threaded connection for carbon and graphite electrodescomprising a threaded member having the contacting surface faces thereofmechanically roughened to provide'a locking between the threadedconnection and to form current-conducting and co-operating surfaces thatreduce the electrical resistance therebetween to a value below that ofsmooth-surface. electrodes of corresponding size.

References Cited :in the file of'this patent UNITED STATES PATENTS1,070,247 .I-Iaines Aug. 12, 1913 2,093,390 Wyckoflf Sept. 14, 19372,135,637 Gade Nov. 8, 1938 2,301,181 Ilsemann Nov. 10, 1942 2,441,188Earhart May 11, 1948 2,484,644 Poupitch- Oct. 11, 1949 FOREIGN PATENTS351,151 Great Britain June 25, 1931 472,856 France Aug. 21, .1914533,761 'Great Britain Feb. '19, 1941

